As for now, one of the most prospective ways of solving the above problem is to carry out simultaneous thermal cracking of oil residues mixed with coal, wherein coal is taken in the amount of 5-30 percent with respect to oil mass (U.S. Pat. No. 4,544,479, 1985; RU, A, 2009166, 1994).
The prior art method includes subjecting the mixture to a light thermal cracking (visbreaking), the main product of which is heavy oil stock with a reduced concentration of metals.
The stock and its distillates can be converted to light oil by catalytic cracking.
The prior art method, however, suffers a number of problems. A relatively low demetalization level provided by this method does not entirely eliminate the problems which arise at further catalytic cracking of the process product, as even in the case of employment of modern metal-resistant catalysts their consumption should be high which adversely affects the cost efficiency of the prior art method.
Another prior art used to solve the aforementioned problem is a method of thermal hydrogen cracking of heavy oil residues, which is referred to in literature as the Aurabon-process (Edward G. Haude, Gregory G. Ionompson, and Robert E. Denny, The Aurabon process: a valuable tool for heavy oil conversion, presented at the AOSTRA Conference, Edmonton, Alberta, Canada, Jun. 6-7, 1985). The advantage of this process is its technological flexibility: modification of the process conditions (temperature, pressure, contact time, etc.) allows the conversion degree and the yield to be varied. Under the most stringent conditions of the Aurabon process, the treatment of black oil from Voskan oil yields, in percentage by mass: gas 5.6, gasoline 4, diesel distillate 14, vacuum gas oil 65, residue 13. Gasoline and diesel distillate are used for further refinement to produce fuel components.
A complicated and yet unsolved problem with the thermal hydrogen cracking is the possibility of coke deposition on the apparatus walls, requiring a periodic stopping of the process and adversely affecting its technical and economical properties.
Most closely approaching the present invention is a method of producing fuel distillates from oil residual stock, including mixing the oil residual stock with sapropelite and a liquid aromatic additive, subjecting the resulting mixture to hydrogen or thermal cracking, and extracting desired products. (RU, A, 2057786, 1996; RU, A, 2076891, 1997). In the prior art method, the thermal or hydrogen cracking is carried out on a mixture containing a heavy oil stock (tars, mixtures of West-Siberian oils, oils from Romashka and Ukhta fields and heavy oil from Bouzatchi field in Mangyshlak), sapropelite (Leningrad or Baltic sulfurous shale or Kuzbass sapromixite) in the amount of 1 to 10 percent by mass, and shale oil or its fraction boiling at 220-340.degree. C. in the amount of 1 to 10 percent by mass at increased temperature and pressure, with subsequent extraction of fuel distillates. The yield of fuel distillates is 56-60 percent by mass with respect to the feed stock after being subjected to thermal cracking and 90 percent after being subjected to hydrogen cracking. Using the hydrofining process, the thermal and hydrogen cracking distillates may be refined to light motor fuels, including motor gasoline and diesel fuel.
The problem with the prior art method is the employment of tetralin or alkyl derivatives thereof as the aromatic additive. Liquid products containing tetralin or alkyl derivatives thereof and their mixtures with other hydrocarbons are produced by hydrogenating technical products containing condensed aromatic hydrocarbons, mainly naphthalene and alkyl derivatives thereof. The process of producing tetralin and its alkyl derivatives is quite costly, consequently, the final product is relatively expensive also. The high price of tetralin hinders the employment of the prior art processes in the oil processing industry.